"Our operators love it so far," Steve Hanson, a national fleet sustainability manager for the company, told Obama about the truck. "They like the quiet, they like the visibility, and they like not smelling diesel fumes."

"That's terrific, keep up the good work," Obama said. He moved on to an AT&T truck, then onto Verizon's hybrid Silverado.

"Nice to see AT&T and Verizon sort of side-by-side," Obama said.

Last stop was UPS and a set of white and brown delivery trucks. The white version was a plug-in, all-electric vehicle; the brown was a "low emission hybrid electric vehicle."

But something was amiss. Obama turned to the white truck, noting its strange lack of pigment. "It's not brown," he said.

It's a test vehicle, he was told. Phew!

From the pool report: "Pool is unable to estimate a carbon footprint for the excursion, but the calculation should take account of the scores of police cars deployed along the route, and all the cars idling in traffic."